1. Field of the Invention
The present invention generally relates to methods and systems for determining one or more characteristics of a pattern of interest on a specimen.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail.
Defect review typically involves re-detecting defects detected as such by an inspection process and generating additional information about the defects at a higher resolution using either a high magnification optical system or a scanning electron microscope (SEM). Defect review is therefore performed at discrete locations on the wafer where defects have been detected by inspection. The higher resolution data for the defects generated by defect review is more suitable for determining attributes of the defects such as profile, roughness, more accurate size information, etc.
Metrology processes are also used at various steps during a semiconductor manufacturing process to monitor and control the process. Metrology processes are different than inspection processes in that, unlike inspection processes in which defects are detected on a wafer, metrology processes are used to measure one or more characteristics of the wafer that cannot be determined using currently used inspection tools. For example, metrology processes are used to measure one or more characteristics of a wafer such as a dimension (e.g., line width, thickness, etc.) of features formed on the wafer during a process such that the performance of the process can be determined from the one or more characteristics. In addition, if the one or more characteristics of the wafer are unacceptable (e.g., out of a predetermined range for the characteristic(s)), the measurements of the one or more characteristics of the wafer may be used to alter one or more parameters of the process such that additional wafers manufactured by the process have acceptable characteristic(s).
Metrology processes are also different than defect review processes in that, unlike defect review processes in which defects that are detected by inspection are re-visited in defect review, metrology processes may be performed at locations at which no defect has been detected. In other words, unlike defect review, the locations at Which a metrology process is performed on a wafer may be independent of the results of an inspection process performed on the wafer. In particular, the locations at which a metrology process is performed may be selected independently of inspection results. In addition, since locations on the wafer at which metrology is performed may be selected independently of inspection results, unlike defect review in which the locations on the wafer at which defect review is to be performed cannot be determined until the inspection results tor the wafer are generated and available for use, the locations at which the metrology process is performed may be determined before an inspection process has been performed on the wafer.
While it is true that metrology is generally inspection independent and mostly driven by sites that are either critical or friendly for measuring morphology of polygons and defect review is generally inspection dependent and driven by sites at which defects have been detected, that may not always be the case. For example, in the case of inspection driven metrology, inspection results can be used to guide selecting sites that are abnormal from all available metrology sites. In another example, review can also be performed without inspection by using sites selected by taking simulation or design driven sites and then using the defect review tool to simply collect images for those designated sites. Examples of such methods and systems are illustrated in U.S. Pat. Nos. 7,711,514 to Park et al, issued on May 4, 2010, and 8,559,001 to Chang et al. issued on Oct. 15, 2013, both of which are incorporated by reference as if fully set forth herein.
In general, defect detection is performed with inspection tools as described above and then additional measurements such as critical dimension (CD) measurements performed with a SEM are performed on a fixed sample of locations. There are, however, a number of disadvantages for the currently used methods and systems for generating a sample for defect review or metrology, For example, sources of variation that impact yield relevant attributes of product circuit patterns may not be practically observable due to substantially low area and pattern coverage of CD SEMs and insufficient sensitivity of inspection tools that use thresholding techniques.
Accordingly, it would be advantageous to develop systems and methods for determining one or more characteristics of a pattern of interest on a specimen that do not have one or more of the disadvantages described above.